SHEAR TEST FOR INDUSTRIAL POWDERS
The shear test should simulate the circumstances in which the powder behave in an handling equipment. Only the size of the specimen is small but, all other circumstances should be the same as in the handling equipment, such as pressure humidity and others.
For many processes, the mechanical properties of powders are responsible for the behavior of the powders. The mechanical properties can be achieved by measuring the shear stress. Measuring the shear stresses by various pressure, we achieve an boundary over which the forces can not grow. This boundary we call YIELD LOCUS. The diagram presenting the yield locus as function of the shear stresses and the pressure is called DIAGRAM OF MOHR. Depending of circumstances there is possible that other inter-particular forces then frictional forces, like cohesive, electrostatic, magnetic, forces Van-Der-Walls, magnetic and others, influences the behavior of powders. This forces predict the position of the Yield locus in the diagram of Mohr.
The properties of the powder can be vary during the process and coarse problems if changes leads to more cohesive powder. Powders can be changed in required direction by mixing other components or treat the powder mechanically or chemically. The shear test can monitor this changes and help us to find the right mixture, treatment or watch over the changes during the production.
Applications of shear test in the industry
- Quality control – for the production of powders - for industrial applications the flowability index of the powders is monitored to ensure trouble-free operation.
- Classification of powders – for the engineering department - the cohesion, angle of internal friction or the flowability index are the generally accepted characteristics for the classification of powders.
- Specification the purchasing department – the purchased powders may vary from supplier to supplier and may have seasonal changes or other influences. Purchase specification of flowability index and the checking of the incoming powders can ensure trouble free operation.
- Specification for sales department – delivery of powder with flowability certificate will satisfy most clients and prevent many complains.
- Material engineering R&D – the required properties of a powder can be developed by varying the parameters of the powder. Changing the parameters and selecting the right mixture of the powders, enables the optimal powder properties to be found for the optimization the process.
- Design of handling equipment – engineering department - for some storage and conveyor equipment, mathematical models exist which require appropriate mechanical powder properties. The shear test provides these parameters for a wide range of applications. The static and technological calculations contribute to safe and reliable process equipment.
- Safety of installations - static calculation – of silos and transport equipment, based on measured powder properties, such as wall friction, density, internal friction and unconfined compressive strength, can guarantee that the calculations are made with the correct powder properties. In this way the shear tester contributes to the safety of the installations.
- Technological calculations of the process equipment requires the powder properties. The correctly determined powder properties will ensure the proper working of the installation only then if the raw materials are checked and are found to correspond with the purchase specification. During the process the powder can be controlled and held within the limits of the process specification.